20W Stereo Audio Amplifier -MAX9744

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Blue4Life
 
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20W Stereo Audio Amplifier -MAX9744

Post by Blue4Life »

I wanted to know how many amps can I run the 20W Stereo Audio Amplifier -MAX9744 if I am using a 12v power supply, and if possible post a schematic for a 12v power supply

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adafruit_support_mike
 
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Re: 20W Stereo Audio Amplifier -MAX9744

Post by adafruit_support_mike »

20W = 12v * 1.66A.

I'm afraid we don't have any designs for a 12 power supply, but there are hundreds of them online.. everything from precision battery-powered units to repurposed computer power supplies.

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Blue4Life
 
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Re: 20W Stereo Audio Amplifier -MAX9744

Post by Blue4Life »

Isn't that too high? I feel it would burn the board if I run it that high.

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Re: 20W Stereo Audio Amplifier -MAX9744

Post by adafruit_support_mike »

Nope. The board is designed for 20W output with supply voltages up to 14v.

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Blue4Life
 
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Re: 20W Stereo Audio Amplifier -MAX9744

Post by Blue4Life »

What would happen if I run it on 12v 2amps?

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Re: 20W Stereo Audio Amplifier -MAX9744

Post by adafruit_support_mike »

In general, electronic devices use however much current they need at a given voltage.

A 12v @ 2A power supply is able to keep up with devices that want 2A when their supply voltage is 12v, but that's all. It won't push 2A through a device that wants less. The MAX9744 wants about 1.6A when the supply voltage is 12v, so that's all it will pull from the power supply.

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Blue4Life
 
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Re: 20W Stereo Audio Amplifier -MAX9744

Post by Blue4Life »

Thanks for the help

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gbuggy79
 
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Re: 20W Stereo Audio Amplifier -MAX9744

Post by gbuggy79 »

I have this amplifier and I have it hooked up to 20W 4Ohm speakers (also purchased from Adafruit). When I power it with my digital power supply at 12V, it never draws more than 80mA, and the audio is a lot quieter than I'd expect 20W to be. The volume pot is turned all the way up, and the audio file I amp playing is even normalized to nearly 200%. My power supply is set to 12V and the Amp limit is set to 2.0.

So it seems like it is putting out less than a watt through the speakers: 12v * 0.08A * 0.93efficiency = 0.89W

Am I doing something wrong?

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Re: 20W Stereo Audio Amplifier -MAX9744

Post by adafruit_support_mike »

Post a photo showing your hardware and connections (800x600 images usually work best) and we'll take a look.

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gbuggy79
 
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Re: 20W Stereo Audio Amplifier -MAX9744

Post by gbuggy79 »

Here are some pics of my test rig.
I figured out how to set the volume on the Raspberry Pi that I am sourcing the signal from, and it is much louder, but it still isn't drawing anywhere near 20W of power.
I used the command 'amixer set PCM -- 0400' to set the Pi's volume to 100%

I took a video of the power supply in action: https://www.youtube.com/watch?v=D71G3sbgLaI
Right at the beginning of the guitar solo (0:17), you can see the power spike to 1.07A/12.8W, but you can see that it usually stays below 10W.

Image
Image

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Re: 20W Stereo Audio Amplifier -MAX9744

Post by adafruit_support_mike »

There are a couple of things that could be involved.

First, we're still not sure how much actual voltage swing you're getting out of the RasPi. It might be putting out standard line voltage, which is around +/-1v. That's still kind of low by the MAX9744's terms.

Second, it looks like your power supply is using the same kind of ciruit used in multimeters.. most likely a dual-slope measurement. Those give good results, but they're slow. It looks like yours updates about four times per second, which isn't fast enough to catch the highs and lows of a complex audio signal.

To measure the true peak current you'd need an oscilloscope or a moderately complicated peak-tracking circuit and a sense resistor.

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